This invention relates generally to manufacturing methods and apparatus for electrical contacts, and more particularly, to methods and apparatus for induction heating electrical contacts.
Electrical and electronic devices generally include circuitry and components which are electrically connected to operate the devices. Typically, the circuitry includes electrical contacts that are mechanically attached, surface mounted and/or soldered to a circuit board. A substrate material of each of the electrical contacts is generally coated with a conductive alloy coating to enhance the soldering characteristics of the electrical contacts. Tin and tin alloy coatings have been used to coat the substrate materials due to the low cost, anti-corrosion, and solderability properties of the tin and tin alloy coatings.
However, the tin and tin alloy coatings have the problems of tin whisker growth and poor solderability due to reactions between the tin and the substrate material. To overcome the problems of tin whiskering and poor solderability, the tin coating is heated until the tin is reflowed. The benefits of the reflowed tin result from microstructure changes and stress relief in the coating and substrate material.
One conventional process used to reflow the tin coating involves the use of a reflow oven to heat the electrical contact and the tin coating. One type of reflow oven is a convection oven. Anther type of reflow oven is an infrared heating oven. However, the problem with the reflow oven is that the entire electrical contact is heated and the process is relatively slow to induce the reflow of the tin. Additionally, once the contacts are removed from the oven, the contacts are shaped, stamped and/or trimmed to a final form, thus exposing the substrate material on areas of the contact such as the edges. The exposed substrate causes solderability problems during assembly of the electrical device. Moreover, convection reflow ovens are also used to melt the tin plating on the contacts, but the time required to heat the contacts causes the tin plating to flow around the contact. As a result, the tin plating thickness may be modified and the overall product performance may be affected.
Another conventional process used to reflow the tin coating involves the use of an induction heater to heat the substrate and the tin coating. The process involves supplying a stock of material pre-coated with tin to the induction heater. Once the tin is reflowed, the stock is shaped. However, during the shaping process, the substrate material is exposed from the shearing and bending process. The exposed substrate causes solderability problems during assembly of the electrical device. As a result, the electrical contacts manufactured in the conventional induction heating processes are not suitable in soldering applications.